1. Field of the Invention
The present invention relates to an optical deflector used in a laser printer and the like, and an optical scanner having the optical deflector.
2. Description of Related Art
FIG. 17 shows a general laser printer 200. As shown in FIGS. 17 and 18, an optical scanner 202 of box shape is disposed within the laser printer 200, and a light beam is emitted from a light source 204 disposed in a side wall of the optical scanner 202.
The light beam passes through a collimator lens 206, is reflected by one reflection face of a polygon mirror 214 constituting an optical deflector 212, and inputted to a surface of a photoconductive material 220 used as a drum-like recording medium via fθ lens 216 and cylindrical mirror 218, so that a latent image is formed on the photoconductive material 220.
As shown in FIG. 19, the optical deflector 212 is secured to the optical scanner 202 and a rotating body 222 including the polygon mirror 214 of the optical deflector 212 is rotatable. On the other hand, a printed board 224 constructed form a metal is secured to the optical scanner 202, and is provided with an integrated circuit 226 driving and controlling the rotating body 222.
A housing 228 of the optical scanner 202 is sealed with a cover 202A or the like to prevent contamination of optical lenses such as the fθ lens 216 (see FIG. 18) disposed in the optical scanner 202. However, it is often made of a material having a low thermal conductivity such as resin because of its low cost and constructionally has difficulty in expelling heat within the housing 228 to the outside.
A rise in the temperature of the housing 228 would exert a bad influence on not only the life of the bearing part 230 of the optical deflector 212 and the reliability of the integrated circuit 226 but also the optical lenses mounted in the housing 228.
Particularly, for optical lenses made of resin, since they have a high thermal expandability, a rise in temperatures would exert a great influence on them. Thermal deformation of the bottom wall of the housing 228 might change relative positional relationships among the light source 204, the optical deflector 212, and optical lenses such as the fθ lens 216, and the photoconductive material 220 as shown in FIG. 18 and deteriorate their optical properties.
A temperature distribution within the housing of the optical scanner is shown in FIG. 20. The temperature distribution within the housing shows that the surface temperature of the integrated circuit mounted on the printed board of the optical deflector is the highest, followed by the surface temperature of the rotation shaft of the optical deflector, and the surface temperature of optical lenses such as fθ lens.
Therefore, radiating a larger amount of heat of the integrated circuit of the optical deflector leads to reducing a rise in the temperature of the housing. A method of radiating heat generated by an integrated circuit on a printed board is described in Patent Reference 1. According to it, as shown in FIG. 21A, a radiating member 236 is brought into contact with the face of a printed board 232 on which an integrated circuit 234 is not mounted, a through hole 242 is formed in a bottom wall 240A of a housing 240 of an optical scanner 238, and the radiating member 236 is projected outside the housing 240 through the through hole 242, whereby heat of the integrated circuit 234 is radiated.
As another method, as shown in FIG. 21B, the radiating member 236 is mounted on an upper face of the integrated circuit 234 to radiate heat of the integrated circuit 234. According to Patent Reference 2, as shown in FIG. 21C, a radiating member 248 made to communicate with the outside of a housing 246 of an optical scanner 244 is brought into contact with a lower face of a printed board 250 and an upper face of an integrated circuit 252 to radiate heat of the integrated circuit 252 and the housing 246.
[Patent Reference 1]
Japanese Published Unexamined Patent Application No. Hei 6-75184
[Patent Reference 2]
Japanese Published Unexamined Patent Application No. Hei 11-242177
However, since laser printers are becoming higher in image quality and printing speeds are becoming faster, when a rotative polygon mirror is fast rotated to scan a laser beam on a photoconductive material, currents consumed by a rotating body and integrated circuits become larger in proportion to the speed of the rotating body as shown in FIG. 22, heat generated from an optical deflector increases, and the temperature of the housing of an optical scanner also rises.
On the other hand, a metallic printed board has an insulating film formed on a metallic board on which a wiring pattern is formed, and connects the wiring pattern and an integrated circuit by solder. Therefore, as shown in FIG. 21A, when the radiating member 236 is brought into contact with the face (back) of the printed board 232 on which the integrated circuit 234 is not mounted, an insulating film (not shown) intervenes between the integrated circuit 234 and the back of the printed board 232, so that heat of the integrated circuit 234 cannot be directly radiated.
In recent years, since miniaturization of an optical deflector has shortened the distance between an integrated circuit and a rotative polygon mirror, as shown in FIG. 21B, if the radiating member 236 is mounted on the upper face of the integrated circuit 234, the wind sound of the rotative polygon mirror 254 rotating fast becomes louder, so that the noise of an optical scanner 256 becomes a problem.
Furthermore, in recent years, small and flat integrated circuits are mounted on the surface of a printed board and are not structured to have a radiating member mounted therein. Therefore, in cases where a radiating member is secured by an adhesive having an excellent thermal conductivity, the thermal resistance of the adhesive and the time required until the radiating member has been secured become a problem.
On the other hand, although there is a method of using tightening members such as screws to mechanically tighten and secure a radiating member to an integrated circuit, holes for the tightening members must be provided on a printed board, so that a securing method becomes complicated and the printed board becomes large in size.
On the other hand, as shown in FIG. 21C, in cases where a radiating member 248 is made to communicate with the outside of the housing 246 of the optical scanner 244 and the radiating member 248 is brought into contact with the upper face of the integrated circuit 252, a method of securing the radiating member 248 and the integrated circuit 252 has the same problem. In addition, the large radiating member 248 is brought into contact with only the upper face of the integrated circuit 252 on the printed board 250 mounted in high density, and must be positioned while maintaining electrical insulation with other electronic parts (not shown) on the printed board 250. As a result, the radiating member 248 has a complicated positioning structure, which causes a rise in costs. Even if the radiating member 248 is flat in shape, it is inevitable that the wind sound of a rotative polygon mirror 258 rotating fast increases.